This invention relates to an apparatus for measuring variable quantities such as fluid pressure, stress and strain and, more particularly, to an apparatus for measuring or supervising the variation in the variable quantity over a long period of time.
The pressure of fluid, for example oil, has been measured statically by means of a Bourdon-tube gauge but the device can not measure a rapid pressure variation such as a surge pressure or the like. Accordingly, for measuring the surge pressure or the like a method has been proposed wherein a pressure-electric converter is used to convert pressure into an electric signal and the electric signal is recorded on a magnetic tape recorder. However, in an ordinary oil pressure operated machine or apparatus there are so much data to be measured that it is difficult as well as expensive to measure and process such large amount of data with the apparatus utilizing pressure-electro converters. Such problems also exist where it is necessary to measure or supervise other variable quantities such as stress and strain over a long period.